by Doyle Rice, USA TODAY

by Doyle Rice, USA TODAY

The deadly twister that ripped through a subdivision near Granbury, Texas, was one of up to 10 that touched down in northeastern Texas Wednesday night, the National Weather Service in Fort Worth said Thursday.

The storms, which left six people dead and scores injured, were the nation's deadliest tornado outbreak in more than a year, the Weather Channel reports. This is the deadliest tornado outbreak since April 14, 2012, when six people died in a tornado in Woodward, Okla.

A preliminary report Thursday morning from a weather service damage survey team in Granbury found EF-4 damage on the Fujita Scale of Tornado Intensity. This means that wind speeds were 166 to 200 mph. EF-4 is the second-highest level on the scale; only EF-5 damage is considered to be worse.

AccuWeather reported that another tornado grew to as large as a mile wide at times.

The weather service will continue to conduct damage surveys throughout the day to determine the exact strength of the tornadoes.

The storms were the result of a strong disturbance diving into northern Texas, AccuWeather meteorologist Anthony Sagliani said. Warm and humid winds blowing from the Gulf of Mexico collided with hot and dry winds from west Texas, resulting it a twisting motion in the lower atmosphere.

As of Thursday morning, there were no tornado watches or warnings anywhere in the nation. The next chance for thunderstorms in Texas will be Sunday afternoon.

The tornado outbreak Wednesday was easily the deadliest of what had been a calm season for tornadoes so far. Prior to Wednesday, only three people had been killed this year in the U.S., in three separate tornadoes, one each in January, February and April, according to the Storm Prediction Center in Norman, Okla.